I am trying to use the audio ports only of the Diamond VC500 that I own with Audacity. I have captured hundreds of tapes using that and AmarecTV. The issue that I am having is trying to capture audio only with Audacity. I select the same audio capture device as I do with AmarecTV, but when I record, Audacity seems to find nothing. Now, if I open AmarecTV and start recording, I can capture just the audio with a blue screen of video and split it from there. I think that is too much work, but will do so if I have to. Please let me know if you have any suggestions for capturing audio.

Demuxing the audio from the video (after you captured) takes a matter of seconds. I don't see the problem.
Just make sure you are capturing PCM(LPCM) audio. 44.1 if it will let you....but 48k is not a problem.